The present invention relates to electromagnetic brakes in general, and more particularly to improvements in electromagnetic brakes of the type wherein the brake is disengaged in response to energization of one or more solenoids. Still more particularly, the invention relates to improvements in electromagnetic brakes of the type wherein the rotary component is non-rotatably secured to a rotary member (e.g., to the shaft of a motor, engine or another machine) which must be braked from time to time, the stationary component is non-rotatably secured to a wall, bearing plate or another stationary member of a motor, engine or another machine, and the stationary component includes one or more permanent magnets which tend to maintain the brake in engaged condition and one or more solenoids which are energizable to effect or assist in disengagement of the stationary and rotary components.
In presently known electromagnetic brakes of the above outlined character, the rotary component is movable axially into and from frictional engagement with a liner or a like friction generating element of the stationary component which is fixed to the stationary member so that it cannot perform any angular and/or other movements with respect thereto. When the solenoid is deenergized, the permanent magnet attracts the rotary component toward and maintains the latter in frictional engagement with the stationary component. Energization of the solenoid results in establishment of an electromagnetic field which opposes the force of the permanent magnet and can be assisted by springs to repel the rotary component from the stationary component so that the rotary component is free to turn with the rotary member, e.g., with the shaft of a motor or engine.
It happens quite frequently that the braking action must be interrupted for relatively short intervals of time, e.g., during a change in setup of a machine tool or the like. In conventional electromagnetic brakes, such interruption of braking action can be achieved solely by energizing the solenoid in the casing of the stationary component, i.e., an attendant cannot manipulate the brake in order to move the rotary component away from the stationary component. This presents problems and causes undesirable delays, for example, when the brake is disconnected from the source of electrical energy, either due to failure or breakdown of the energy supply or because the energization of solenoid could endanger the attendant or attendants. Moreover, prolonged disengagement of the brake during a change of setup by energizing one or more solenoids would entail unnecessary waste in electrical energy.